As used in this disclosure, a host device, which may be a laptop computer, a personal digital assistant (PDA), a digital cellular telephone, or any other device adapted to perform two-way communication of information using the now well known Internet Protocol (IP), is considered to be “portable” when the device can be moved from one location to another, and operate at either location. A portable device does not have to operate WHILE it is being moved. On the other hand, a device is considered to be “mobile” when it can not only operate in different locations, but it can also operate WHILE it is being moved from location to location. If a device is adapted for mobile operation, it is, by definition, portable. Accordingly, in the following description, the use of the term “mobile host” will include both situations where the host is mobile (being moved) as well as where the host is in an area served by a foreign network.
Dynamic Host Configuration Protocol (DHCP) is the current dynamic addressing and configuration protocol in widespread use on the Internet. See R. Droms, Dynamic Host Configuration Protocol, RFC2131 Draft Standard, March 1997. DHCP not only enables hosts to acquire addresses but also other configuration options associated with the access network (e.g., netmask for subnet, domain name servers, directory servers, email servers, etc.) See S. Alexander and R. Droms, DHCP Options and BOOTP vendor Extensions, RFC2132 Draft Standard, March 1997. As emerging and future client applications increasingly rely on network services, the ability to dynamically configure these services through options becomes important. The DHCP protocol is a popular tool for today's service providers to manage their addressing needs.
While DHCP was originally intended for use with fixed hosts, it was a natural candidate to support dynamic addressing in the context of a host that would be portable and/or mobile. Since DHCP was designed for fixed hosts, its use on mobile hosts presented a number of challenges. Many of DHCP's limitations in supporting host mobility have been well documented in the literature, although none of such efforts have focused on dynamic home addressing which is the target of this invention. See, for example, Charles Perkins and Kevin Luo, Using DHCP with Computers that Move, Wireless Networks Journal, vol. 1, pp. 341-353, 1995; Jon-Olov Vatn and Gerald Maguire Jr., The effect of using co-located care-of addresses on macro handover latency, in Proceedings of Nordic Teletraffic Seminar, August 1998; Jon-Olov Vatn, Long random wait-times for getting a care-of address are a danger to Mobile Multimedia, IEEE Intl. Workshop on Mobile Multimedia Communications, pp. 142-144, November 1999; and A. McAuley, S. Das, S. Baba and Y. Shobatake, Dynamic Registration and Configuration Protocol (DRCP), http://search.ietf.org/internet-drafts/draft-itsumo-drcp-00.txt, October 1999.
In an attempt to enable seamless mobility of a host device while retaining Internet connectivity, the Mobile IP protocol (M-IP), as described by Charles Perkins in IP Mobility Support, RFC 2002 Draft Standard, October 1996, was developed. The prime goal of M-IP is to enable mobile hosts to get connected to the Internet and remain connected WHILE they move. This connectivity is preserved in a “transparent” manner, that is, in such a way that it prevents the disruption of networked applications running on the mobile host while it moves. To accomplish this goal, M-IP relies on the ability to configure the device's IP address to match that of the subnet onto which it is attached at any point in time, since having the correct address is needed to ensure that packets get routed to the host.
In M-IP, a mobile host has a fixed home address and acquires an additional care-of address (COA) that is updated as the host changes its location, called a “point of attachment”. M-IP allows two options regarding the placement of a COA agent, also called the Foreign Agent (FA); the agent may be present inside the network (for example, at the base station) or as a co-located care-of address (CCOA) at the mobile host. While M-IP relies on the ability to configure the home and care-of addresses, it does not dictate how they are to be obtained.
In the early stages of M-IP design, portable and/or mobile hosts had fixed home addresses that were statically configured. Recently, the trend has shifted to a dynamic home addressing model, where a configuration protocol, which could be DHCP or some other protocol, enables these hosts to dynamically acquire and install a home address on power-up. Dynamic home addressing enables efficient management of addresses, which is critical in supporting wide-area wireless data users with millions of devices using the limited address space dictated by the IPv4 standard. It also provides ease of configurability, by replacing the burdensome task of manually configuring hosts with a more effective mechanism for address allocation. Note that the IPv6 standard removes address space limitations but it also stands to benefit from the configurability advantages awarded by dynamic addressing support.
One problem, however, that has been overlooked is that dynamic home addressing required when mobile hosts power up in a foreign network is not specified in the M-IP standard. Specifically, mobile hosts that power up in a foreign network with no home address cannot contact addressing servers in their home network through the type of “broadcasting” contemplated by DHCP. An alternative arrangement is needed that works, is compatible with DHCP and M-IP, and is easy to implement.